In recent years, as semiconductor devices have been highly integrated, circuit patterns of LSI devices contained therein have been increasingly made finer. Fine processing of the patterns requires not only thinner line widths simply but also improvements in dimensional accuracy and positional accuracy of patterns. Semiconductor memory devices called memories are not an exception. In memory cells formed with the free use of high-accuracy processing technologies, it has been continuously desired that a certain amount of charge required for storage is held within a narrower region.
Various memories such as DRAMs, SRAMs and flash memories have been produced up to now. These memories all use a MOSFET in a memory cell and accordingly fine processing of patterns causes a need for an improvement in dimensional accuracy at a higher rate than the rate of fine processing. Therefore, the lithography technology of forming these patterns is imposed with larger loads, which become a factor in increasing the lithography process cost that occupies the major part of the current mass production cost, that is, a factor in increasing the product cost (see Non-Patent Documents 1 and 2, for example).
On the other hand, a technology of basically resolving the problem on such fine processing may comprise artificially synthesizing a desired molecular structure and using the uniformity of the resultant molecules to form uniformly characterized elements in a trial. There are large problems on the technology of arranging the synthesized molecules at a desired position and on the establishment of electric contact with the arranged electrode. In addition, such the element serves as the memory using an extremely small amount of charge and accordingly has a problem because of an extremely large probability of malfunctions that may be caused by disturbances such as natural radiations.
Further, from the viewpoint of effective utilization of energy resources, it has been desired to suppress power consumption in semiconductor devices as low as possible. Memories are not an exception. Particularly, in the case of the memory, a memory cell portion occupies a large proportion. Therefore, it is important to suppress power consumption in each memory cell. Power consumption is represented by the product of voltage and current. Accordingly, if a voltage is fixed at around 1 V due to anti-noise measures and so forth, an extremely small current is required to achieve lower power consumption.
[Non-Patent Document 1]
    Applied Physics, Vol. 69, No. 10, pp. 1233-1240, 2000, “Semiconductor Memory; DRAM”[Non-Patent Document 2]    Applied Physics, Vol. 69, No. 12, pp. 1462-1466, 2000, “Flash Memory, Recent Topics”